Correlations of Leaf Water Content, Canopy Temperature and Spectral Reflectance in Perennial Ryegrass Under Drought Stress.

Accurate, rapid, and non-destructive estimates of drought stress occurrence and plant water status are important in developing site-specific irrigation management for the purpose of water conservation while maintaining turf quality. This research was designed to determine whether changes in canopy temperature and canopy reflectance under drought stress could be used to predict turf quality and plant water status in perennial ryegrass (Lolium perenne L.) The six cultivars (Brightstar, Catalina II, Divine, Inspire, Manhattan 4, and Silver dollar) of two-year-old perennial ryegrass were subjected to drought stress in a field in West Lafayette, IN. The grass was mowed at 2.5 cm and fertilized at 134 kg N ha^-1. Irrigation was withheld and the soil was allowed to dry down at different cycles from May to August 2007 (the first phase of the experiment). The drought-stressed grasses fully recovered prior to the next dry down cycle. Data were taken prior to drought stress and during dry down periods on a daily basis or at two-day intervals. The individual plot was 3 by 3 m with four replicates. Across all cultivars, changes in canopy reflectance were generally observed when leaf relative water content dropped to about 5 to10 %. Leaf relative water content was correlated with turf quality (r = 0.82***), canopy temperature (r = -0.55***), and normalized difference vegetation index (NDVI) by (R880-R650)/(R880+R650) (r = 0.78**). Canopy temperature was correlated with turf quality (r =-0.66***) and NDVI (r =0.66***), respectively. NDVI and canopy temperature models can be used to predict drought stress and indicate leaf water status in perennial ryegrass.